The present invention relates generally to sensors and more particularly to a sensor with a non-uniform spatial sensitivity.
There is a constant need to improve the performance of digital cameras. A typical digital camera has an array of charge coupled devices (CCD), which occupies an area A at the image plane of the camera to capture an image. As shown in FIG. 1, the array is typically made up of many detectors arranged in a grid with a period T, and with each detector occupying an area having a dimension r. The array is exposed for a time t to capture the image. If T is equal to r, the resolution of the captured image would depend on T. In many situations, r is smaller than T, and the array is translated during the image capturing stage to obtain a higher resolution image. In those circumstances, the resolution of the captured image depends on r--the smaller the r, the higher the resolution.
In order to use a detector with a small r, one typically either needs many more detectors to fill up the Area A at the image plane, or to step the array at a high resolution in both the X and the Y directions to capture information in the entire image. Unfortunately, both methods have their weaknesses. In the first method, as the number of detectors increases, the price of the array goes up dramatically. In the second method, with the stepping at a high resolution, one needs to have many more steps to cover the entire image. Since the image is captured in time t, the more steps the array takes to capture the image, the less time the array has for each step. Thus, as the number of steps increases, the array gathers less light for each step, which translates to an array with a low sensitivity. For example, replacing a first 1,024.times.1,024 CCD with a second 512.times.512 CCD in the area A of the image plane could reduce the sensitivity by sixteen times. This is because the second CCD occupies about 1/4 of the area and is exposed about 1/4 of the time as compared to the first CCD.
It should be apparent from the foregoing that there is still a need to capture images with an inexpensive detector array that has good resolution and sensitivity.